SYNTHESIS AND PROPERTIES OF CAGE-TYPE S-BRIDGED COIIIZNII POLYNUCLEAR COMPLEXES - CRYSTAL-STRUCTURE OF SPONTANEOUSLY RESOLVED [(CO(AET)3)4ZN4O]BR6 (AET= 2-AMINOETHANETHIOLATE)

The reaction of fac(S)-[Co(aet)3] with ZnBr2 in water produced a cage-type S-bridge polynuclear complex with a "complete" core [Zn4O]6+, [{Co(aet)3}4Zn4O]Br6 (2), by way of a precursory cage-type complex with a "defective" core [Zn3Br]5+, [{Co(aet)3}4Zn3Br]Br5 (1). 2 was subject to spontaneous resolution and its crystal structure and absolute configuration for the (+)580CD isomer were determined by X-ray crystallography. [{Co(aet)3}4Zn4O]Br6.9.5H2O, chemical formula C24H91N12O10.5S12Co4Zn4Br6, crystallizes in the cubic space group P2(1)3 with a = 18.981 (1) angstrom, V = 6838.6 (3) angstrom 3, Z = 4, R = 0.0478, and R(w) = 0.0448 for 1844 reflections with F(o) > 5-sigma(F(o)). The four octahedral fac(S)-[Co(aet)3] subunits are bound to the tetrahedral [Zn4O]6+ core in a tetrahedral arrangement, and each Zn(II) is tetrahedrally coordinated by three thiolato sulfur atoms from three different fac(S)-[Co(aet)3] subunits and a central mu(4)-oxygen atom. For the (+)580CD isomer, chiral configurations are regulated to LAMBDA for all four fac(S)-[Co(aet)3] subunits and R for all 12 bridging sulfur atoms, giving an approximate T symmetrical structure. Cyclic voltammetric measurements in water exhibited four consecutive quasi-reversible redox couples in the region of -0.3 to -0.9 V (vs Ag/AgCl) for 2, which correspond to the four Co(III)/Co(II) redox reactions, while 1 exhibited four nonreversible reduction waves in the same potential region. The electronic absorption and circular dichroism (CD) spectral behavior of these complexes are discussed in comparison with those of related mononuclear and linear-type S-bridged trinuclear complexes.